This invention relates to an antenna operable in two frequency bands and, more particularly, to a planar dual frequency band antenna for use in a handheld communications device.
In recent years, portable handheld wireless communications devices have become increasingly popular. At the present time, cellular telephones operating in the frequency band of 824 MHz through 896 MHz are the most widespread type of such devices. However, the personal communications system (PCS) operating in the frequency band of 1850 MHz through 1990 MHz is gaining in popularity. Accordingly, equipment suppliers are developing portable handheld radio transceivers which operate in both these frequency bands. Thus, there exists a need for an antenna capable of operating in both of the described frequency bands.
Handheld portable radio transceivers must be designed in accordance with certain human factors considerations. Thus, such a device should be compact and lightweight. It is known to design such a device with a rod (or whip) antenna which is selectively retractable into, or extendable out of, the device case. It is also known to design such a device with a short fixed helical antenna extending out of the device case. However, such an extending antenna possesses certain disadvantages. Thus, for example, having an antenna extending out of the case detracts from the smooth contours of the case. Further, such an antenna can present problems when placing the transceiver into a user's pocket or purse. Thus, there exists a further need for a dual frequency antenna which does not suffer from the foregoing disadvantages.
It is known to provide such transceivers with two antennas. One of the antennas (the primary antenna) is used for both transmitting and receiving signals. The other antenna (the diversity antenna) is used only for receiving signals. The received signals from both of the antennas are added together according to a certain known scheme. The use of a diversity antenna is intended to mitigate the effects of multipath fading. The general idea is that if two incoming waves are out of phase and cancel each other on one antenna, on the other antenna this cancellation will not occur or will not be as complete. In order to achieve this effect, the two received signals must be statistically uncorrelated. It would not be desirable to have two extending antennas on the device because this would be unaesthetic. More importantly, for the diversity scheme to function, the two antennas either have to be placed far from each other, which is impossible considering the size of the handheld device, or they have to be as different as possible, providing different antenna patterns. It is known to provide a planar inverted F-antenna as a diversity antenna on a handheld transceiver, but all such known devices have been only for a single frequency band. Thus, there exists another need for a dual frequency antenna which can be utilized as a diversity antenna.